1. Field of the Invention
The present invention relates to a magnetoresistive element exhibiting giant magnetoresistive effect, and a thin film magnetic head, magnetic head slider, head gimbal assembly, head arm assembly and a magnetic disk device provided with the magnetoresistive element.
2. Description of the Related Art
A thin film magnetic head, which includes a magnetoresistive element (MR element) exhibiting magnetoresistive effect (MR effect), is widely used for reading out information written on magnetic recording media such as a hard disk. Recently, a thin film magnetic head including a giant magnetoresistive element (GMR element) exhibiting giant magnetoresistive (GMR) effect is more general because of increasing recording density of magnetic recording media. Examples of such GMR element include a spin valve GMR element (SV-GMR element).
The SV-GMR element is configured as a stacked layer in which a magnetic layer whose magnetization direction is fixed in a given direction (magnetically pinned layer) and a magnetic layer whose magnetization direction is varied in accordance with an external signal magnetic field applied from outside (magnetically free layer) are stacked with a nonmagnetic interlayer in between. In particular, those configured to make a read current flow in a direction along a stacking plane of the element during reading operation is called CIP-GMR element (Current in Plane GMR element). Further, a thin film magnetic head including the CIP-GMR element is called CIP-GMR head. In this configuration, electric resistance (namely, voltage) is varied when the read current is applied in accordance with a relative angle between the magnetization directions of the two magnetic layers (the magnetically pinned layer and the magnetically free layer).
To comply with higher recording density of magnetic recording media in recent years, CPP (Current Perpendicular to the Plane)-GMR head, which includes a CPP-GMR element that is configured to allow read current to flow in a direction orthogonal to the staking plane during reading operation, has been developed. Such CPP-GMR head generally includes a GMR element, a pair of magnetic domain controlling layers that are arranged to face each other in a track-width direction, sandwiching the GMR element with an insulating layer in between, and a bottom electrode and a top electrode that are arranged to face each other with the GMR element and the pair of magnetic domain controlling layers in between in a stacking direction. The upper and lower electrodes also serve as top and bottom shielding layers, respectively. Such CPP-GMR head has an advantage in that high power is available when reducing the dimension of element in the read track width direction, as compared with the CIP-GMR head. Namely, in the CIP-GMR head, since read current flows in a direction along the stacking plane of the element, dimensional reduction in the read track width direction results in the narrowing of magnetic sensitive area through which the read current passes, thereby decreasing the amount of change in voltage. On the other hand, since read current passes through the CPP-GMR head in the stacking direction, the dimensional reduction in the read track width direction less affects the amount of change in voltage. For this reason, the CPP-GMR head is advantageous compared with the CIP-GMR head in view of reduction of track density, whose unit is “TPI” (tracks per inch). What is more, since insulating layers are omitted between the CPP-GMR element and top/bottom shielding layers, that allows the reduction, by the thickness of the omitted insulating layers, of the linear recording density, whose unit is BPI (bit per inch), as compared with the CIP-GMR head.
There is also a tunnel MR element (TMR element) that is configured similar to the CPP-GMR element in that the read current flows in the direction orthogonal to the stacking plane. This TMR element includes an ultra-thin insulating layer called tunnel barrier layer so as to obtain much higher resistance change ratio than that of the above-mentioned CPP-GMR element. For this reason, the thin film magnetic head including the TMR element (TMR head) is highly expected to comply with a further improvement of recording density.
As disclosed in JP2004-31545A, JP2006-49358A, or JP2006-179566A, for example, for the purpose of giving more uniform bias magnetic field to a magnetically free layer in the track width direction, GMR element with what is called in-stack bias structure, in which one magnetic domain controlling layer is stacked on a magnetically free layer instead of a pair of magnetic domain controlling layers arranged to sandwich the GMR element in the track width direction, is proposed.